Apparatus for conducting ion exchange operations



2517;051 APPARATUS FOR couwc'rmc ION momma ormnons Filed June 3, 1949 IAu 1, 1950 w. R. swsflsou 5 Sheets-sheet 1 INVENTOR Walter R SwansonATTORNEY A g- 950' w. R. SWENSON 2,517,051

' APPARATUS FOR couwc'rmc 10m mzcumqz orm'rlous Filed June 3. i949 5Sheets-Shoat 4 INVENTOR Walter R. Swanson ATTORNEY 1, 1950 w. R. SWENSON2,517,051

APPARATUS FOR CONDUCTING ION EXCHANGE OPERATIONS Filed June 3, 1949 5Sheets-Sheet 2 ATTORNEY APPARATUS FOR counuc'rms ION EXCHANGE ormwxonsFiled June a, 1949 Aug. 1, 1950 w. R. SWENSON 5 Sheets-Sheet :5

a ma m w E Mm m 0 W M Q mm w om k Q R om f a 8 km 3 wk ww R k \Nm. m 1%R E wk 7 m k II. QM. mm/ mDh h m NW 7 %m m mm Mb k w hb H m %\W H QQM. k\MQ y a. m9 w m l W R K m u 1 Q 3 f mm 3 9w m9 k9 L q A 0 s w. R.swsnsou 2,517,051

APPARATUS FOR CONDUCTING mi Excuses opmnons Filed June 5. "1 949 5Sheets-Sheet; 5

s B A r 2 P Reset Reference Pressure- Peset Pressure L 4 6 ProportionalBand Control P010! 5 E Adjustment Pressure 0 (PEA) 1 f 3 Need/e ValveMeasured Wr/w/e 1 5 .MMLMedM/Q Pfe5$Uf y I I t P essure g1.

' Fig. 6;

6 Pilot Nozzle Pressure Supp/y Pressu e 5 R Valve Pressure t w?INVENTOR. I Walter R.

Swenson ATTORNEY Patented Aug. 1, 1950 UNITED STATES PATENT OFFICEAPPARATUS FOR CONDUCTING ION EXCHANGE OPERATIONS Walter R. Swenaon,Flushing, N. r., anignor to The Don- Company, Stamford, Conn, acorporation of Delaware Application June 3, 1949, Serial lilo. 97,026

2 Claims. (Cl. 210-44) above, to maintain the liquid level as close asappurtenances is also called or known as an ion exchange cell or brieflya cell.

It is desirable and important in the operation of such cells that theliquid level be maintained in the cell at or only slightly above the topof the bed, so that substantial submergence of the bed is insured, yetso that the accumulation of any substantial excess liquid volume abovethe bed is avoided.

More specifically, therefore, this invention relates to control devicesfor automatically maintaining the liquid level in the cell substantiallyconstant and in a predetermined or desired relationship to the top ofthe bed. i

A known level-control device utilizes primary control impulses derivedfrom a float mounted on the container and actuated by the fluctuationsof the liquid level. That is to say the location of the float or floatdevice in eflect determines the normal level which it is desired to havemaintained in the tank. In other words, once the disposition of thefloat device is flxed on the container or tank, that location in turnsubstantially determines the top level, and hence the depth of the bedof exchange material in the tank, and vice versa. In the known device anoutlet valve or throttling device discharging the treated or effluentliquid from the cell is controlled through relay means by the primarycontrol impulses emanating from the float device. These relay effectsvary the setting of the efliuent valve automatically in accordance withand in a manner to compensate for the fluctuations of the liquid level.Such a known control mechanism operates to correct an undue rise or fallof the liquid level by correspondingly increasing or decreasing theeffective through-flow area of the eflluent valve or throttling deviceand thereby decreasing or increasing the through#flow resistancethereof.

More specifically, in the known control device the movements of thefloat are utilized to vary the admission of pressure of an auxiliary airpressure supply to a pressure-responsive diaphragm which in turn adjuststhe setting of the eiiiuent throttling valve. That is, rising of thefloat causes an incremental opening of the eiiluent valve, while fallingof the float causes incremental closing of the valve.

Although it is desirable, as has been stated possible to the top of thebed while insuring its submergence, the functioning of the floatnevertheless requires a depth of liquid above the bed well in excess ofa desirable minimum, that is a depth, for example, in a practicalinstance of about 6 inches. The effect of that undesired excess liquidvolume is characterized by its proportion relative to the liquid voidvolume, that is the volume in the void spaces in the bed of granu withthe known float-controlled device. Indeed, i it is the object to reducethe excess liquid volume required for maintaining the control eflective,from the 6 inches previously required to a range of 1" to or even less.

Another object is to provide an improved autornatic level control devicewhich permits varying 'the control level by simple adjustment, that iswithout necessitating structural changes in the disposition orrelocation of the control devices relative to the tank. With such acontrol device it should be permissible to increase or decrease thedepth of the bed as the need arises, and by simple adjustment to shiftthe normal level to be maintained by the device, that is the referencelevel, by an amount corresponding to a desired change in the depth ofthe bed. In other words, such an improved level-control device: shouldrender the engineering determination of the depth of the bedsubstantially independent of the structural disposition of the levelcontrol devices; it will therefore do away with the need for certainstructural dependencies and render more flexible engineeringdeterminations and plant lay-out.

Still other objects are to provide control devices which avoidmechanical apparatus limitations by the use of hydraulically actuated orpressureresponsive impulse-translating means. and which lend themselvesto remote control in the sense that they can be mounted a reasonabledistance away from the tank, for example in connection with a centralcontrol panel serving a plurality or battery of exchange cells; and inconnection with such remote control to provide means for visualindication of the liquid level, and capable of being associated with thecontrol panel.

According to the concept of this invention the liquid level ismaintained close to the top of the bed by measuring hydraulic pressurevalues proportionate to the fluctuations of the level, rather thanallowing a float device to translate the fluctuations of the levelmechanically to the relay means and then to the eilluent valve.

According to this concept the liquid level is maintained close to thetop of the bed by measuring or registering fluctuations of the liquidlevel in terms of pressure changes. To this end this invention proposesto derive pressure values proportionate to the level fluctuations byutilizing the hydraulic head represented by the level as a measurablepressure value that changes with a change of the liquid level andrepresents the variable to be regulated. Diil'erentials of that valuerepresenting variations of the liquid level are relayed to effect aproportionate correctiv setting of the eflluent valve of the cell.

This concept provides for what is herein termed a pressure probe orpressure tap in the nature of a gas bubble pipe immersed to a suitabledepth into the body of liquid in the cell and mainly into the bed ofexchange material itself. The depth of immersion of this probe or taprepresents the hydraulic pressure head which must be overcome by auniform supply of auxiliary gaseous medium or compressed air that isbeing forced through the pipe at a controlled slow' rate. This auxiliarymedium, herein also called the purging or pressure gauging fluid,bubbles up through the liquid against the static hydraulic head as wellI as against whatever air or gas pressure may be I acting upon thesurface of the liquid. Such surface pressure may be the pressure of theatmos phere when the tank is of the open type or it may besuper-atmospheric when the tank is of the closed type with a pressureaircushion of a desired constant pressure being maintained above theliquid.

The pressure of the bubble air represents a measure of the hydraulichead that varies with the liquid level. That is to say, an absolutemeasure of the variations of the liquid level in terms of varyinghydraulic pressure or static head is obtained by deriving thedifferential between the higher pressure registering from the bubblepipe and the lower pressure acting upon the surface of the liquid, sincethat diflerential is the value of the static head per se as representedby the depth of immersion of the bubble pipe.

Referring to the example of the closed type tank, in order to derivethis pressure difierential, this invention proposes to provide theaforementioned high pressure tap together with a low pressure tap, thelatter in the form of a pipe extending into the freeboard or air cushionspace in the tank and similar to the high pressure tap dischargingpressure gauging or purging fluid (air) into the freeboard space. Thediflferential of these pressures from both taps represents the variableto be measured, regulated or controlled and to be utilized as an impulsefor effecting the control or compensatory setting of the ellluent valveproportionate to the magnitude of the impulse. The control system fortransmitting the pressure impulses from the pressure taps to theeflluent valve is implemented by certain control equipment units whichare known per se and are commercially obtainable.

4 Again, taking the closed type or tank as an example, there is suppliedindependently to each of the pressure taps a uniformautomaticallycontrolled flow of compressed air. That is to say,

each tap is supplied with this auxiliary gaseous medium or agent througha flow-control device which per se is known and the function of which isto supply the gaseous medium or fluid or compressed air at a rate thatis constant irrespective of change of the pressure against which thatmedium is being supplied. The principle of such a fiow-rate-controllingdevice is that it effects flowcontrol automatically by responding tochanges in the pressure diflerential across an orifice. That is to say,this flow-rate or metering devir utilizes the pressure diil'erentialprinciple which is biased upon the flow of liquid or of gas through aconstriction or orifice. The difierential of the pressures before andafter the orifice isutilized to efiect control or metering of the airsupply to the orifice and to the pressure taps in proportion tofluctuations of such pressure differential. This metering pressurediilferential may herein be termed the orifice pressure differential asdistinguished from the main pressure differential or pressure impulsewhich for the purpose of this invention is to be derived from the liquidlevel or static head conditions in the tank, and which is herein termedthe tap pressure differential. One such flow control device is providedfor each pressure tap to automatically maintain a constant orificepressure differential for each tap and such a device is therefore hereintermed a constant differential flow-control device or briefly a constantflow controller.

The implementation of the control system further providespressure-transmitting and pressure-magnifying relay devices or unitswhich receive the pressure impulses caused by variations of the tappressure difierential, which impulses adjust the eflluent valve of thetank in a manner to maintain the liquid level therein. These relaydevices comprise a difierential pressure transmitter unit, and further avalve-actuating controller unit which in turn is relay-controlled by thetransmitter unit. That is to say the pressures derived from each of thetwo pressure taps in the tank and from the flow controllers reach thedifferential pressure transmitter unit which evaluates the differentialof these tap pressures and transmits a value corresponding to the tappressure diflerential to the valve-actuating controller unit which inturn utilizes it to control through relay air pressure the diaphragm oithe tank effluent valve and thus to maintain the liquid level in thetank at a predetermined height. Again, the differential pressuretransmitter unit as well as the controller unit each per se are knownand commercially obtainable.

The function of the relay units of this control system is based upon anddue to the interaction of air pressure received by them and of relay airpressures transmitted by them. That is to say, a common source ofconstant auxiliary or relay air pressure may be provided for the relayoperation of the various units of this control system. Hence, suchauxiliary air-pressure provides the purging or gauging air that passesthrough and is controlled by the two constant flow-controllers. Thereaction pressures of the purging air from these flow-controllers inturn react upon the differential pressure transmitter unit so that thesame will emit a corrective impulse corresponding to the value of thetap pressure difierential whatever its varying magnitude may be.

8 Auxiliary air pressure from the aforementioned source is also suppliedto the differential pressure transmitter unit which through it isinfluenced to emit and impart proportionate control pressure impulses tothe controller unit.

Again, air pressure from the aforementioned auxiliary source is suppliedto the valve-actuating controller unit and the magnitude of this relayair pressure is such that it will properly influence the pressureresponsive diaphragm adjusting the eiiiuent valve of the tank formaintaining the liquid level therein at the desired point. The functionof the valve-actuating controller unit is to modify the control pressureimpulses which it emits in proportion to andsubstantially'instantaneously with the control pressure impulsesreceived by it from the differential pressure transmitter unit. In thisway the controller unit acts to automatically restore and hold theliquid level in the tank at that pre-deter! mined reference level forwhich the controller .is adjusted and it will thus operate whenever anysufllcient deviation or fluctuation of the liquid level should furnishand initiate the primary impulses for the operation of this controlsystem.

It is an important feature in the operation of this liquid level-controlsystem that the valveactuating controller unit embodies means wherebyits control response is adjustable so as to maintain automatically andwithin practical limits whatever reference level it is desired to havemaintained in the tank. Thatis, a simple adjustment on the controllerwill shift the reference level either upwardly or downwardly to a newpoint at which it is to be maintained in the tank by the controllerunit. Once the controller unit has been adjusted to operate on the basisof a desired reference liquid level in the tank, the

controller will then automatically and continually compensate for anyfluctuations of the level and thereby maintain a'desired referencelevel.

In the drawings: 1

Fig. 1 is a diagrammatic overall view of the level control systemoperatively interconnecting the tank with the eflluent control valvethereof.

Fig. 2 is a cross-section of the tank on line 2-2.

Fig. 3 is an enlarged view of the control de vices of the system of Fig.1, showing vertical sections of the devices such as the constant flowcontrollers, the differential pressure transmitter, and the controllerunit.

Fig. 4 is a further enlarged sectional detail view of one of theconstant flow controllers and of the diiferential pressure transmitterof Fig. 3.

Fig. 5 is a further enlarged sectional view of the controller unit ofFig. 3.

Fig. 6 is a still further enlargement of the Fig. 5 sectional view ofthe flow controller, illustrating the operating pressures within thisunit.

An ion exchange cell I in Fig. 1 is represented by a closed tank It inwhich a bed of granular ion exchange material herein briefly called theion exchange bed is indicated at ll supported by a perforated plate i2usually called a constriction plate. The tank itself is of the closedtype and comprises a cylindrical body portion II, a top portion I4 and abottom portion I5. An inlet pipe It leads into the tank at an elevationthat substantially corresponds to the top of the ion. exchange bed. Thisinlet pipe I 8' has a flange connection I! with the tank as well as witha distributing header l8 disposed within the tank.

The distributing header l8 shown in its plan view in Fig. 2 comprises amain or header central portion I! having lateral openings 20, and branchheaders 2| extending laterally and horizontally from the main headerportion and having outlet openings 22. Liquid to be treated in the ionexchange cell or tank by contact with the ion exchange material entersthe tank through v the intake pipe It to be distributed by the header I8substantially uniformly over the cross-sectional area of the bed II. Thefeed of liquid into the tanli as well as its discharge from the tank issuch that the bed remains substantially submerged at all times duringits operation.

The liquid passes downwardly through the bed through the perforatedsupporting plate 12 into a collecting chamber 23 formed by the plate l2and the tank bottom l5, hence the liquid passes from the tank through adischarge or eflluent pipe 2|. An effluent control valve unit 25 isprovided in the discharge pipe 24 and is controllable or adjustable byair pressure acting upon a diaphragm indicated at 26. valve unit isknown per se. Its action for the present purpose is such that an.increase of air pressure reaching the diaphragm will tend to close thevalve whereas a decrease of air pressure upon it will tend to open thevalve. An increment in the valve-opening will cause the liquid level inthe tank .to fall, while a decrease will cause it to rise.

An air cushion is maintained within the tank, that is in the closedspace, and for maintaining such a cushion at a predetermined desiredconstant pressure, there is indicated a pressure air supply line 21leading to the top of the tank. The pressure of this air cushion isautomatically kept at a desired constant value as indicated by anautomatic pressure control valve 28 with its pressure gauge 28a.

THE LIQUID LEVEL CONTROL SYSTEM The control system proper operativelyinterconnects the tank ID with the effluent control valve unit 25through a series of interacting air pressure responsive control deviceswhich constitute component units of the control system, these units perse being known and commercially available. The control system starts atthe tank ill with a pair of pipes herein calledv pressure taps, namely ahigh pressure'tap and a low pressure tap as represented by a pair ofpipes 29 and 30 respectively leading into the tank by way of a flangeconnection 3|. The high pressure tap has an open end 25a for airdischarge and extends downwardly into the bed of ion exchange material,for example a suitable distance d1 from the top face of the bed.Auxiliary air herein also termed pressure gauging or purging fluidpasses from pipe 29 against pressure which is the sum total of thestatic pressure head of the liquid column di and the pressure of the aircushion above. The low pressure tap 30 has an open and 30a normallyunsubmerged for the discharge of purging air into the air cushion space.At the opposite end the control system has an air pres- 'suretransmitting pipe 32 leading to and con- Such diaphragm controlledconstant flow controller 34 for the low pressure tap 33, a diilerentialpressure transmitter 35 and a flnal controller unit herein brieflytermed the controller 33.

The two constant flow controllers 33- and 34 continuously supplyauxiliary air to the pressure taps 23 and 33 respectively at a rate offlow which is kept constant by these flow controllers irrespective ofvariations of counter pressure in the tank It). The difierentialpressure transmitter 35 evaluates the pressure differentials between thehigh pressure tap 23 and the low pressure tap 33 and emits a.pressureaccording to that diflertial to the controller 33 which in turntranslates it proportionately into relay air pressure for actuating theeilluent valve 25 with the net result of compensating for any variationsof the liquid level in the tank in order that this level be maintainedsubstantially at a desired predetermined point, namely at the top faceof the bed H.

The constant flow controller 33 (for the high pressure tap) in turnconsists of a pressure con-' trol device 33' and a metering device 33',while the constant flow controller.34 (which has a component controlunit is identical to the constant flow controller 33) for the lowpressure tap 33 consists of a pressure control device 34 and a meteringdevice 34". The pressure control device 33 in turn has a pressureresponsive diaphragm 33 upon which it relies for its operation.Similarly the pressure control device 34 has a pressure responsivediaphragm 34 The metering device 33" has an adjustable orifice 33through which the purging air must pass and upon which it relies for itsoperation. Similarly the metering device 34 has an adjustable orifice 34The pipe or high pressure tap 23 leads from the tank Hi to a branchpoint 3'! connecting with a pair of branch pipes 38 and 33. The branchpipe 38 has a pair of sub-branches 38 and 38 leading to the constantflow controller 33, that is to the pressure control device 33 and to themetering device 33 respectively. The pressure control device 33 isfurthermore operatively interconnected with the metering device 33 by anair-flow pipe 43. The pressure control device 33 is supplied withauxiliary pressure air through a pipe 4|. The auxiliary air thussupplied passes through the pressure control device 33", then throughpipe 43 to and through the metering device 33 leaving it by way of pipe38* and passing on through branch pipe 38 and past branch point 31 intothe high pressure pipe or tap 29 to issue from the open end 28 thereof.As will be explained further below the differential of pressure beforeand after the orifice 33 of the metering device 33 influence thepressure control device 33 in such a manner that the flow or purging airto the high pressure tap 23 is keptconstant irrespective of pressurevariations in the tank.

Similarly the low pressure pipe or tap 33 leads from the tank to abranch pipe 42, and thus into a pair of branch pipes- 43 and 44 The pipe43 leads to a sub-branch point 45 and thus into a pair of sub-branchpipes 45* and 45 which lead to the pressure control device 34 and to themetering device 34 respectively. The pressure control device 34'-isfurthermore operatively interconnected with an air passage pipe 46.Auxiliary air pressure is supplied by a pipe 41 to the pressure controldevice 34' and passes therethrough and then by wayof pipe 43 to andthrough the metering device 34'. Controlled air-flow from the meteringdevice 34 then reaches the low pressure tap 33 by way of the pipes 45and 43. Again, the difierential of pressures before and after theorifice 34 influences the pressure control device 34'- in such a mannerthat the flow of purging air to the low pressure tap 33 is maintainedconstant irrespective oi pressure variations within the tank.

The pressure air supply for the constant flow controllers 33 and 34 maybe derived from a common source such as is indicated by a branch point33 joining the air supply pipes 4| and".

The diil'erential pressure transmitter 35 evaluates the pressuredifierential between the high pressure tap 23 and the low pressure tap33 herein termed the tap diilerential. Any variations of the tapdifl'erential in turn are proportional and correspond to variations ofthe liquid level in the tank. The differential pressure transmitter 35responding to the tap diflerential or else to variations of the liquidlevel sends an actuating pressure representing the tap difierential andherein termed the measured pressure to the controller 33 which in turnsends a corresponding controlling relay air pressure to the eiiluentvalve 25 so that eventually the eflluent area of the valve I may beeither increased or decreased as the case vice 43.

may be in proportion to the impulse received due to any variations ofthe liquid level in the tank with the net result that the liquid levelis maintained substantially at a, desired predetermined point.

The diilferential-pressure transmitter 35 as a unit comprises adiflerential-pressure responsive Sylphon device 43 and a pressure relaydevice 53 functionally interacting with and controlled by the Sylphondevice 43. The operation of the Sylphon device 43 is in turn based uponthe interaction of an upper Sylphon 5| with a lower Sylphon 52, bothSylphons H and 52 being interconnected yet separated by a floating'plateof septum 53. Pressure reaction from the high pressure tap 23 reachesthe interior 54 of the upper Sylphon 5| by way of pipe 33, whilereaction pressure i'rom the low pressure tap 33 reaches the chamber orspace 55 surrounding these Sylphons by way of pipe 44. Any variation inthe tap pressure diilerential, that is a variation of the liquid levelin the tank thus manifests itself in a corresponding slight upward ordownward movement of the floating plate 53.

The relay pressure device 53 receives auxiliary air pressure by way ofan air supply pipe 53. Auxiliary air may pass through an air passagepipe II into the Sylphon device 43 then through an air nozzle 53 intothe interior 53 of the lower Sylphon 52 whence it may discharge throughan air passage pipe 33. Auxiliary air may pass from the relay pressuredevice 53 by way of an exhaust valve 3| controlled by the variations ofthe tap pressure differential received by the Sylphon de- The functionof differential pressure transmitter 35 is such that itrespondsinstantaneously to transmit a measured pressure proportional to the tappressure differential to the controller 33 which in turn respondsinstantaneously to transmit relay control pressure to the eiliuent valve25 for correcting any undue variations of the liquid level in thetankl3.

- That is to say the measured pressure proportional to the tap pressuredifferential is transmitted to the controller 33 through a pressuretransmitting pipe 32 which leads from ajunction point 33 of pipes 34 and33. This measured pressure operates within the controller 33 to vary aJusting member 89 having at its outer end a handle 90 and at its innerend a thorn it which is thus adjustable up and down for varying thethrough-flow area of the orifice 33 provided in the lower stufling box88. The upper stufllng box I! has a ball check valve 92 leading into anoutlet chamber 83 disposed in the head portion source, this beingindicated by the pipe 56 ioining pipe 84 at a junction point II, thisJunotion point in turn being interconnected with junction point 68 bypipe 1, and being supplied from a common source'of pressure airindicated at.

Details of construction, function, and interaction of the componentcontrol units 33, 34, II, and 38 (i. e. the two constant flowcontrollers,

the difierential pressure transmitter, and the final controller for the-eiliuent valve) will be presented in the more detailed description ofthe control system that follows.

DETAILED DESRIP'IION OF 'I'HE CONTROL SYSTEM A. Tm: CONSTANT FLOWCONTROLLER (1) Structural description As constant flow controller units33 and 34 are alike in principle, it will herein suifice to describe theconstant flow controller 83 and its function as representative. Asmentioned above this unit comprises a pressure control device 83 and ametering device 33. Auxiliary air or purging fluid p2 sses from pipe 4|through the pressure control device 33, then through air passage pipe t.to and through the metering device 33' and finah; through the highpressure pipe or tap 29 to a point of submergence in'thetank I0, issuingin bubbles from the lower end 29 of the tap.

The pressure control device 33- comprises a body portion 69 and a top orcover portion Ill, between which portions is confined a diaphragm "M.Above the diaphragm ii is a pressure chamber l2 while below thediaphragm is a pressure chamber 73. The upper pressure'chamber 12 may betermed the low pressure chamber being connected through pipe 38 to thedownstream side of the metering device. The lower chambar 713 may betermed the high pressure chamber being connected through pipe 40 withthe upstream or high pressure side of the orifice M The upper chamber 12has disposed in it a coil spring M which is a compression springconfined between the cover member 10 and the diaphragm ii I, and whichbecause of its function within this device is being termed thediflerential pressure spring. The lower chamber 13 has a passage 15leading to pipe 40, another passage I8 leading to a valve chamber 11 inwhich is disposed a valve member 18 sustained by a light spring 19 justsufficient to balance the seat of the valve member. A passage 80connects the valve chamber H with the air supply pipe ll.

The metering device 33* comprises a body portion 8| having a headportion 83 and a foot portion 82, both head and foot portions beinginterconnected by a vertical glass tube 84 the top and a closed oil atthe bottom by a screw cap member 88 into which in turn is threaded anorifice ad- 81 and closed by a screw cap member. Purging air passingfrom pipe 40 into the metering device ll must pass through the inletchamber t1 and through the orifice 33, then upwardly through the glasstube 84 past the ball check 02 and outlet chamber 93, andout throughpipe I. and pipe or tap 2!. Within the glass or transparent tube 84 is afiow indicator member or floating plug 85 kept in suspension by theupward flow of air in the tube. The position of this floating member 95indicates the flow. intensity or rate of upward air-flow through thetube and its magnitude can be defined by a scale 96 provided upon thebody portion 8| of the metering device.

ing device 33', equal to the compressive pressure (2) Functionaldescription For the purpose of maintaining a constant rate of flow ofpurging air to and through the pressure tap 28 the pressure controllerdevice'li' co-acts with the metering device 33 in such a manner that aconstant pressure difierential is maintained between the upstream sideand the downstream side of the orifice 33 irrespective of variations ofthe counter pressure within tank Ill. That is to say, when this orificepressure difierential decreases due to an increase in counter-pressure,that increased pressure will depress the diaphragm H and with it thevalve member I8 to reduce the throttling efiect of valve member I8 forair passing from the valve chamber 11 through passage 18 to the meteringdevice or upstream side of the orifice 33. This will restore the desiredorifice pressure diflferential.

Vice versa when the counter-pressure for tap 29 decreases, the upstreamorifice pressure in chamber 18 will force the diaphragm "H upward- 1ypermitting the valve member 18 to fall and accordingly, to throttle theflow through passage 18.

purging liquid to orifice 33 and past to needle valve member 89 of themetering device 33'.

Thus the pressure control device 33' maintains a constant differentialpressure across the metervalue of the spring 14 and independent ofvariation of the pressure upstream or downstream of the needle valvemember 89.

B. THE DIFFERENTIAL Panssuan 'I'RANSMITTER (1) Structural description Asstated above the differential pressure transmitter 35 comprises aSylphon device 49 and the that each change of the tap pressurediil'erential As will be seen fur-,

. are connected to the floating plate 59.

l 1 received by it as impulse is instantaneously trans-, 'lated into aproportionately higher relay pressure transmitted to the controller 99for actuating the eiiluent valve 25. That is the booster pilot valveunit 59 brings in a higher or relay air pressure placed under theinfluence oi the Sylphon device99 in such a mannerv that variations ofthe tap pressure differential received by the Bylphon device will varythe relay pressure in proportion.

This proportionately increased -or diminished pressure constitutes whathas above been termed the measured varlable pressure transmitted to thecontroller unit 99 in which it acts again through the medium of a relayfluid pressure supply to the controller, and which proportionatelyactuates the eiiiuent diaphragmcontrolled valve 25 in a compensatoryfashion correcting varia- I tions of the liquid level in tank I9.

' The Sylphon device 99 comprises a housing 91 having a cylindrical bodyportion 99, a bottom portion 99, and a top portion I99, which housingcontains a difierential pressure-responsive systemor,

combination of expansion diaphragms-so-called Sylphons or bellows. Thiscombination of Sylphons comprises the upper largediameter bellows plate59 and its lower end to the bottom portion 99 of the housing 99. Thusthere are established an annular inner pressure chamber I92 between thebellows 5i and I9 I, the outer annular pressure chamber 55 surroundingand represented by the space between the Sylphon combination or bellowsand the surrounding housing assembly, and the pressure chamber 59 withinthe lower bellows 52. The upper inner pressure chamber I92 communicateswith the pipe 39 (and thus with the high pressure tap 29) through a portI 99 in the top portion I99 of the housing. The outer annular pressurechamber 55 communicates with the pipe 99 (and thus with the low pressuretap 39) through a port I99 in the bottom portion oi! the housing.

A compression coil spring I 95 acting asa balancing spring is disposedwithin the upper inner bellows MI and is confined betweenthe floatingplate 59 and the top portion I99 01' the housing, the degree ofcompression of the spring'beingadjustable by means of an adjusting screwI99-provided in the top portion I99. The top portion I99 has a tap holeI9'I for the upper inner pressure chamber I92 closed by a cap screw I99and a tap hole I99 for the outer pressure chamber 55' and closed by acap screw H9. The discharge nozzle 58 for relay pressure air is screwedinto the bottom portion 99 or the Sylphon device 99 and extends upwardlywithin the lower bellows 52 terminating at the underside of the floatingplate 59. The floating plate 59 by this arrangement isheld yieldinglyagainst the mouth of air nozzle and oflers resistance to the dischargeof the relay air from the nozzle into the lower inner chamber 59. Thepressure which tends to urge the floating plate 59 against the mouth ofnozzle N varies with variations of the tap pressure diii'erential, andaccordingly varies the resistance oflered by the plate to the dischargeof the relay air from the nozzle.

Relay air pressure is supplied to the nozzle N 'and through pipe 92 withthe controller unit 99.

The booster valve unit 59 comprises a body portion 59" and a top orcover portion 59'' between which portions is conflned the pressureresponsive diaphragm 59. Thus there are established an upper pressurechamber I I I above, and a lower pressure chamber II2 underneath thediaphra m 59. Valve chamber H9 is provided underneath the lower chamberH2 and connects therewith through a passage II9 presenting an invertedvalve seat for receiving -a booster valve member I I5 sustained by acompression spring acting as a weight-balancing spring for the valvemember and confined between the valve member and a cap screwI I9constituting the bottom" of the valve chamber H9. The stem H9 of thevalve member extends upwardly terminating, at the underside .ofdiaphragm 59 to be actuated thereby. The valve stem 9' is surrounded bya compression coil spring I I I which is conflned between the bottom oipressure chamber H2 and theunderside of diaphragm 59. This spring IIIbecause of its function in the operation or this device is termed a,diflerential pressure spring as will be further explained in theoperation of this device.

Relay air pressure, that is filtered air from a constant pressuresource.- is supplied through the pipe 59 to the booster valve unit 59 inwhich it reaches the valve chamber I I9 through a conduit II9. A portionof this auxiliary air may pass from conduit II9 through a branch conduit'9 leading into upper pressure chamber II and having interposed in it ametering oriflce I29.

The body portion 59 01' the booster valve unit is provided with anautomatic bleeder valve 9I comprising a housing portion I2I extendingdownwardly from the booster valve unit and provided at its lower endwith an exhaust opening I22. 'This bleeder valve further comprises avalve member in the form or an expansion diaphragm or bellows I29 thelower end of which is closed and forms a valve portion or thorn I29adapted to open or close the exhaust opening I22 as the bellows I29expands or contracts. Thus there are established in the bleeder valve 9Ian outer pressure chamber I25 between housing portion I 2| and bellowsI29, and an inner pressure chamber I29 within the bellows or expansionvalve member I29. A conduit I 21 connects the outer pressure chamber I25with the diaphragm pressure chamber II2 as well as with the pipe 99.Another conduit I29 connects the interior pressure chamber within thebellows I29 with the upper diaphragm chamber III.

The response of the difl'erential pressure-transmitter 95 to variationsof the tap pressure diflerential is briefly this:

The high pressure'tap 29 connects with the inside of the large bellows5I in the Sylphon device 99, while the low pressure tap 99 connects withthe opposite side, namely with the pressure chamber 55. Any increase, ordecrease oi dinerential pressure across the large bellows II isinstantly balanced by the air pressure in the pressure chamber 59 oi thelower bellows 52 because 01' the function of the booster valve unit 59.Auxiliary air from a supply source of constant pressure filtered airflows throughthe restriction or metering oriflce I29 to the top ofdiaphragm 59 and through pressure chamber III and pipe 51 into theSylphon-unit 99. that is through nozzle 13 N against the resistance offloating plate 53 into the pressure chamber 59, thence to escape throughpipes 50 and 64 back to and through the booster valve unit 50. Havingreturned to the booster valve unit the auxiliary air passing throughconduit I28 reaches the outer pressure chamber I of the bleeder valveI2I and may escape through its exhaust opening I22, even as its pressurereaches the pressure chamber II2 to react upon the underside of thediaphragm 50. At the same time the bellows of the bleeder valve memberI23 is interiorly subjected to the pressure from the top of diaphragm III through conduit I28. Thus the bleeder valve member I23 is subjectedto or balanced or controlled by the pressure from chamber III (beforethe nozzle N) counteracting the pressure in chamber 59 (after the nozzleN).

The auxiliary air from pipe 56 may also be admitted through the pilotwalve, that is from the valve chamber II 3 past pilot valve member II4to underside of diaphragm 50, namely into the lower pressure chamber II2which in turn communicates with the outer pressure chamber I25 of thebleeder valve and thus with the exhaust opening I22. e

Any increase or decrease of differential pressure (that is variation oftap pressure difierential) acting upon the bellows SI and 52 tends tomove the floating plate 53 to or from the mouth of nozzle N, as the casemay be, thereby causing respectively an increase or decrease of pressureupon the top side of diaphragm 50 controlling the pilot valve memberIll. Immediately this pressure change is balanced as air is eitheradmitted through the pilot valve or exhausted through the automaticbleeder valve I2 I. The auxiliary air pressure thus balanced inproportion to impulses from the pressure taps (variations of tappressure difierential) maintains the lower bellows 59 in a condition ofequilibrium with respect to the mouth of nozzle N. Consequently, thebalanced pressure after the nozzle in chamber 59 and pipe 50 representsthe net relay pressure varying in proportion to the tap pressuredifferential received, and thus represents what is herein termed themeasured variable pressure that reacts uponthe controller unit 36 whichin turn transmits proportionate control impulses or relay pressures tothe eflluent valve to compensate for liquid level fluctuation in thetank I0.

It will be seen from the pneumatic circuit or pneumatic system operatingwithin the diiferential pressure transmitter that the pressure in nozzle58 is always higher than the balance pressure oflered by the floatingplat 53 by the amount of force exerted by the spring III under thebooster valve diaphragm which spring ll'l is therefore herein termed adifierentialpressure or pre-loading spring. The differential pressure atthe nozzle mouth, that is the differential between the pressure withinthe nozzle and the pressure in chamber 59 surrounding the nozzle istherefore always the same regardless ofthe pressure in the bellows 5Iand 52, insuring practically the same fixed distance between the nozzlemouth and the floating plate 53.

(2) Functional description If, due to a rise of liquid level, anincreased tap pressure differential reaches the Sylphon device 49, theditferential pressure transmitter will respond as follows:

This increase in pressure through pipe 39 and pressure chamber I02forces floating plate 53 14 downwardly against air pressure from nozzle58 thereby building up pressure in pipe 51 which pressure is that of theauxiliary air supply throttled down through the flxed orifice '3. At thesame time this 'built up pressure reaches the interior of the expansionvalve member I23 through conduit I28, this valve member is normallysufllciently open or balanced or cracked to exhaust an amount of airequal to that normally passing through orifice II9, pipe 51, nozzle 53,pipes 50 and 64, and chamber I25 to exhaust I22.

The thus increased pressure in chamber III of unit 50 depressesdiaphragm 50 thereby depressing pilot valve member Ill thus admittingpressure air from pipe to the underside of diaphragm 50 and at the sametime into outer pressure chamber I25 as well as through pipes 54 and 50into chamber 59 as well as through pipe 62 into chamber I52 ofcontroller unit 35. This pressure in turn because of the previousclosing of valve member I23 continues to buildup act,- ing upon theunderside of plate 53, until it balances the force exerted upon the top01' that plate. Hence, for a given pressure increase imparted to the topof the plate 53, the corresponding proportionate pressure increase isthus imparted to the chamber I52 of controller unit 36 which in turnsets the eilluent valve to compensate for the increase of the level. Inother words the balance of forces between the topand the under side ofthe plate 53 is attained when the difference of pressures in pipes 51and 641 has become equal to the pressure of the spring H! ex-'- ertedupon the underside of the diaphragm 50.

By virtue of the balanced condition being established, the inner and theouter pressure acting upon the exhaust valve member I23 also becomebalanced relative to each other so that again the normal amount ofauxiliary air escapes from exhaust I22, namely, the air which iscontinuously escaping through orifice II 9 and from nozzle 58.

That is to say, because of the initial impulse of the tap pressuredifferential there will now have become established higher pressures inpipes 51 and proportional to the increment of the 1111- pulse receivedalthough the differential of these increased pressures will haveremained the same and equal to the pressure exerted by spring 1. Thusthe pressure of that spring equals the pressure drop across the nozzle58, that is the drop of pressure within the nozzle to the pressurearound the nozzle. I

Vice versa, if due to a drop of the liquid level a decreased tappressure differential reaches the Sylphon device 49, then thedifferential pressure transmitter unit 35 will respond as follows:

This decrease in pressure through pipe 39 and chamber I02 causes thefloating plate 53 to move upwardly away from nozzle 58, therebyreducexhaustvalve member I23 through conduit I28. I

This exhaust valve member is normally cracked, that is held under abalanced inside and outside pressure to be sufliciently open to exhaustan amount of air equal to that normally passing.

through orifice II9, pipe 51, nozzle 58, pipes 60 and 64, and chamberI25 to exhaust I22.

The above assumed decrease of pressure in chamber III insures closure ofpilot valve I. This pressure continues to reduce until it balances theforce on top of floating plate 53. Hence for a given pressure decreaseimparted to the top of the plate 33 a correspondingly proportionatepressure decrease is thus imparted through pipe 32 to the chamber I32 of'the'controller unit 33 which in turn correspondingly sets the effluentvalve.

In other words, again the balance of forces between the topside and theunderside of the plate 33 is attained when the difference of pressureinpipes 31 and 34 has again become equal to the pressure of spring II'Iexerted upon the underside of diaphragm By virtue of this balancedcondition being established, the inner and outer pressures upon theexhausted valve member I23 also become balanced so that again the normalamount of auxiliary air escapes from exhaust I22, namely the aircontinually escaping through orifice II3 and from nozzle 38-.

That is to say, because of the initial impulse of the tap pressuredifierential there 'will now is again in direct proportion to themeasured variable pressure issuing from the diiierential pressuretransmitter 33.

The controller 33 functions in response to varying conditions in thetank II in a manner which will be more fully understood in view ofpressure diflerential spring I23 the tension of which is adjustable by ascrew I33 having a handle knob I3I. This diaphragm D1 is outwardly underthe have become established alower pressure in pipes 31 andproportionate to the change of impulse (tap pressure differential),while the difierential between these lower pressures in pipes 31 and 34will have remained the same and indeed equal to the pressure of springII'I. Thus the pressure of that spring equals the pressure drop acrossthe nozzle 58, that is the drop of pressure within the nozzle to thepressure surrounding th nozzle. The variable pressure transmitted fromthe differential pressure transmitter unit 33 through pipe 32 to thecontroller unit 33 is what is hereinafter termed the measured variable Yin the following description of the controller 33.

C. THE CONTROLLER UNIT (1) Structural description of thecontroller unitThe functioning of the controller unit 33 is to respond to controlimpulses from the diflerential pressure transmitter in such a mannerthat, whenever the control system as a whole is in balance, thecontroller unit 33 transmits to the eilluent control valve 25 a relaypressure for actuating it corresponding to each particular pressure orimpulse sent to it from the differential pressure transmitter 35.However, if the control system becomes unbalanced as a result of achange of the liquid level in tank I3, then the controller 36 will firstattempt to transmit a re lay pressure or force which is in directproportion to the measured variable pressure which it receives from thedifierential pressure transmitter 35. If, because of a sustained changeof conditions in the tank, this does not bring the difierential pressureback to a normal value, that is a value corresponding to a control pointabout which the controller 33 normally operates, then the controllerwill bring into play what is herein termed the reset reference pressurewhich will operate to either increase or decrease the relay pressure orforce which is being sent from the controller to the eiiluent valve 25.This reset reference pressure will continue either to magnify or todiminish this relay force as the case may be until the measureddifierential pressure reaches a value corresponding to the controlpoint. At this time the action of the controller will reverse itself,and the measured diflerential pressure will go beyond the value thatcorresponds to the control point. Consequently, the action of thecontroller 33 will then be the reverse of that just set forth until suchtime that the actuating pressure transmitted from the con troller to thediaphragm of the eiiluent valve 23 pressure of spring I23 as well asunder pressure of the atmosphere. This diaphragm D1 represents a valvemember I32 at its underside which opens or closes an air passage orificeI33 provided in section S1, which orifice connects a pressure chamberI34 at the underside of diaphragm D1 with an exhaust conduit I33. Thediaphragm D1 also carries at its underside a valve disk I33 which opensor closes a conduit I31. The section Si has a needle valve N1 which hasa graduated hand knob I38 by means of which it is adjustable to open orto close or to vary the through-flow passage for air from a conduit I33to a pressure chamber I43.

A second diaphragm D2 is interposed between the sections 81 and S:separating the pressure chamber I43 above from a pressure chamber I42below the diaphragm, the latter chamber I42 communicating with apressure chamber I43 through a constriction or air passage orifice I43.

The diaphragm D2 may operate to open or close an exhaust conduit I43which has interposed in it a constriction or air passage orifice I41.The pressure chamber I43 connects with the conduit I33 through a needlevalve N: which has a graduated hand knob I43 whereby it is adjustable toopen vor to close or to vary the flow passage for air from the conduitI33 into the chamber I43. and this is what will hereinafter also becalled the proportional band adjustment (P. B. A.) needle valve. 1

.The sections 32 and Sa have interposed between them a third diaphragmD: separating the pressure chamber I43 above from the pressure chamberI33 below. A pipe I3I interconnects the chambers m and m.

The sections 8: and 84 have interposed between them a fourth diaphragmD4 separating the chamber I33 above from-a pressure chamber I32 below,the latter chamber receiving through pipe 33 the measured difierentialpressure from the transmitter 33.

The sections 84 and 83 have interposed between them a fifth diaphragm D5which separates the chamber I32 above from a pressure chamber I33 below,the latter chamber communicating directly with the conduit I33.

The diaphragms D3, D4, and D5 constitute a functional unit in that theircentral portions are interconnected and rendered unitary by means of abolt I34 and spacers I33 and I33 provided between respective diaphragms.The lower end oi.

the bolt I34 projects below the diaphragm Do to 17 constitute a valvemember III which may open orclcseanairpsssaaeoriilce llleonnectingthepressure chamber Ill with a pressure chamber I", this latter chamber inturn communicating through a constriction or air passage orifice m withthe conduit Ill.

The sections Se and 85 have interposed between them a diaphragm De whichseparates the chamber Ii! above from a pressure chamber I" below. Thediaphragm Ds hasa dual function in that it not only actuates a valvemember "I, but also in conjunction with the valve member In acts initself as an exhaust valve. That is, the diaphragm Ds has embodied in itan exhaust conduit I" connecting through an air passage oriflce I IIwith the chamber Ill. Relative movement between the diaphragm Do and thevalve stem It! of member I" may either close or open the orifice I" asthe case may be. That is a sufficient upward movement or bulging of thediaphragm Dc will open a flow passage through air passage orifice iii asit moves away from the valve stem I52", and allow the chamber iii toexhaust through conduit m. Conversely, a sutflcient downward movement orbulging of the diaphragm Dc will close the exhaust passage through airpassage orifice I as that orifice closes upon the valve stem "2*. Indeedthe downward movement of diaphragm Ds may be such as to depress thevalvemember III sufficiently against the pressure of a spring "2" toopen air flow passage 165 leading into the chamber Iii from a pressurechamber it. below which latter chamber connects with the pipe 64 thatsupplies relay pressure air. The chamber I", also connects with theconduit I31, while the chamber iii connects with conduit it! and alsowith pressure pipe 32 leading to the diaphragm chamber of the eliluentcontrol valve 25.

(2) Functional description of the controller unit In addition to thedetailed structural description of the controller as shown in Fig. 5,there will now be rendered its operational description or functionalanalysis in terms of pressure impulses received, pressure impulsesemitted, and intermediate pressure eflects manifesting themselves withinthe controller, namely in the various pressure chambers and conduitstherein, and

therefore also manifesting themselves upon the the controller unit maynow be rendered in terms of equations of pressure.

This controller is a commercially available unit which is or. may betermed. a proportional reset controller for reasons whichwill appear inthe course of this functional analysis. At any rate, the purpose andfunction of this controller in its present environment is to impartactuating pressures to the eflluent valve 25 whioh pressures areinproportion to the pressure impulses received by the controller as aresult: of. vari-' ations of the liquidlevel in tank ll. .Acorrective orcompensatory setting of the effluent valve is thus effected tothe end ofmaintaining the liquid level at a predetermined point. For the purposeof this analysis the operational pressure acting 18 within thecontroller have been termed and designated as follows:

Supply pressure (relay air) 3 Control point pressure 0 Measured variablepressure Y Reset reference pressure P Reset pressure L Intermediatepressure 8 Pilot nozzle pressure G Enluent valve pressure B Theseoperational pressures are also in Fig. 6 oi the drawings by theconstrasting manner of shading or the respective pressure areas orspaces in the unit.

The meaning of these operational pressures will explain itself as thisanalysis proceeds.

This is a (Proportional-Reset Controller," which means that its responseto a deviation from the control point (or desired value of the measuredvariable pressure) will manifest itself as an immediate change in theEiiiuent valve' pressure R proportional to the deviation, accompanied bya more gradual change in the Reset reference pressure P. The change inthe valve pressure R (that is the relay air pressure imparted to theemuent valve 25) causes a change in the setting of the control valve 25and that tends to minimize the deviation and bring the measured variablepressure back to the control point. If the cause of the deviation isonly a momentary disturbance or upset, equilibrium will be reestablished as the Measured variable pressure Y returns to itsoriginalvalve. In that case, the Reset-reference pressure P will beginto change only, and then return to its original value. If, however,the'cause of the deviation is some more permanent condition whichrequires a new setting of the control valve to maintain the Measuredvariable pressure Y at the desired value, the Reset reference pressure Pwill continue to change as long as the Measured variable pressure Ydeviates from the Control point pressure 0. A change in the Resetrefence pressure P produces a similar change in the Reset pressure L andIntermediate pressure 8. The effect of this is to permit equilibrium tobe reached with a new value of Valve pressure R but with the Measuredvariable pressure Y in agreement with the Control point pressure 0.

It is important to note here that proportional controller action causesthe eilluent control valve 25 to change promptly by an amountproportional to the deviation of the measured variable pressure from thecontrol point pressure. If

with the new control valve setting but with the Measured variablepressure Y and Control point pressure 0 in agreement.

To see how' the above action is accomplished, assume that the pressuresystem within the controller is in equilibrium which means that Y=O and-S=R, also P==L=S=R. For the purpose of this explanation, suppose thereset rate needle l9 valve is shut oil so the controller will haveproportional action only. Then assume that due to some change in theprocess the Measured variable pressure Y increases by a constant amount.

The downward force exerted by Y on the diaphragm assembly m, D4, D5 isgreater than its upward force by an amount proportional to thedifference in areas of the diaphragms below and above the Measuredvariable pressure Y. The downward force of Y is opposed by the upwardforce of O on an equal area; likewise the upward force of Y is opposedby the downward force of on an equal area. The net result of that is adownward force of K (YO), where K is a constant determined by thedifference in areas mentioned. This downward force tends to close thepilot nozzle and increase pressure G which forces down the pilotdiaphragm D and valve member I62. Then air from the supply B isadmitted, increasing pressure R. When R increases it becomes greaterthan 8 so there will be a flow from R to S throughv the proportionalband adjustment (P. B. A.) needle valve. That increases pressure S whichadds to the downward force on the diaphragm assembly D3, D4, D6 andcauses R to increase further. This continues until R and S have eachincreased to such values that the quantity of air escaping through therestriction between S and L equals the quantity flowing through the P.B. A. needle valve at which time S will no longer increase andequilibrium will be reached. Equilibrium requires that the net downwardpressure on the diaphragm assembly D3, D4, D5 equal the net upwardpressure which is then S+KY=R+KO or RS=K (YO) and S=R-K (Y--,O).

Also S=R (pressure drop across the P. B. A. needle valve). Therefore thepressure drop across the P. B. A. needle valve is K (YO). The flow ofair through any restriction is proportional to the square root of thepressure across the restriction, sothe flow from R to S is proportionalto VK (YO). must go through the restriction between S and L and, as thepressure drop across a restriction is proportional to the square of theflow, pressure S-L is proportional to (VK Y-O); hence. .S'L isproportional to K (YO) so that the following equation may be written:

(where C is a constant dependent on the size of the restriction, thesetting of the P. B. A. needle valve and other constants of thecontroller).

It has been shown above that R=S+K(YO) Furthermore both L and P areequal to the original value of R which may be called R0. Therefore(where (C-l-K) of course, is a constant) and R-RO=(C+K) (YO), but RR0 isthe change in pressure R due to the deviation of the measured variablepressure from the control point pressure (YO), and it has been shownthat the change in valve pressure (R--Ro) caused by the deviation isproportional to the deviation, this being the definition of proportionalaction.

Now assume the P. B. A. needle valve to be wide open so that there ispractically no resistance at that point and, therefore, practically nopressure drop. In other words, the quantity of air escaping through therestriction between S an The same flow.

- L will not equal the quantity flowing through the P. B. A. needlevalve until S is practically equal to R. The effect of that is that foreven a small deviation (YO) S will continue to increase (and cause R toincrease until R reaches its maximum value. Hence, when the P. B. A.needle valve is wide open the proportional band is very "narrow," whichmeans that even a small deviation (YO) will cause a large correctivemovement of the control valve. The more the P. B. A. needle valve isclosed, the wider the proportional band becomes, until when the valve isshut entirely, the deviation (YO) will be balanced by a slight increasein R-just enough to counterbalance the downward force (K (YO) A smallincrease in R will then balance quite a large (YO) because the areaagainst which the upward pressure of R is exerted is quite largecompared to the difference in areas (K). This is the condition whichfurnishes the maximum widt of the proportional band, or, in other words,the minimum corrective action of the control valve (effluent valve) fora given deviation.

So far there has been considered only the proportional action of thecontroller. It has been shown above that when the proportional actiononly is working, there must be a deviation in order to hold the effluentcontrol valve at any setting other than that at the start when theprocess was in equilibrium. Now, assume the condition (described above)when there is a deviation (YO) and the process has become balanced witha new eilluent valve position corresponding to R=S=K(YO) reset rateadjustment (RRA) needle valve 9. small amount, allowing a flow from R toP. P will slowly increase (at a rate dependent on the size of the resetreference volume and upon the amount the RRA needle valveis open). As Pincreases, L will increase (because the restriction between B and L andthe exhaust nozzle covered by the diaphragm between P and L constitute apilot which keeps L balanced with P). As L increases, S will increasebecause of the open restriction between L and S. As set forth above, anincrease in S causes an increase in R, which in turn tends to correctthe process so Y is brought closer to equality with O. This actioncontinues as long as R is greater than P, and equilibrium is reachedwhen R=S,

and Y=O. If a deviation (YO) persists R will continue to increase andwill continue to cause P (and therefore S) to increase until maximum Ris reached. In the usual case, however, the eilect is to increase Runtil the process is brought into balance with Y=O, so that the requiredvalve setting for the new load condition is obtained withoutnecessitating a deviation to keep the valve in the new position. Thatagrees with the definition of Reset action."

All of the above discussion has been on the basis of an increase in thevalue of the Measured variable pressure Y. The same reasoning, however,applies in the case of a decrease in the value of I. In that case, theunbalanced force lifts the pilot and allows some air to escape so Gdecreases. That allows the pilot diaphragm Do to lift and bleed air fromthe Effluent valve pressure R, reducing its value. The same reasoning asbefore will demonstrate similar proportional and reset action which, inthis case, will reduce the valve pressure R in proportion to thedeviation (OY) and, if the deviation per- Then open the sists, willgradually reduce the valve pressure until 0 and Y are brought intoagreement-or until R reaches its minimum.

SUMMARY OF THE FUNCTION OF TH ENTIRE CONTROL SYSTEM There will now bedescribed the total function oi the control system, namely the chain ofeftap pressure diil'erential through the differential pressuretransmitter unit 35, and proportionately increases the measured variableY acting through pipe 82 upon chamber l5! within the controller unit 38.

In that case, due to the internal response of the controller unit 36 (asabove described), that unit will cause a proportionate increase incontroller pressure delivered by it through pip 32 to the diaphragm 25of the ellluent valve. This effect will open the emuent valve furtherand sumciently to allow the level in tank ii to drop to normal. When thelevel has thus returned to normal and the disturbing influence hasdisappeared, that will also cause the valve to return to its formersetting, namely the setting which it maintained prior to the occurrenceof that disturbance.

If a sustained increase of tap pressure diflerential should occur, thenthe internal response of the controller unit 36 (due to its automaticresetting of the reference pressure P as above explained) will be suchas to further increase the control pressure in line 12 until it hasincreased the efliuent valve opening sufllciently to bring the liquidlevel in the tank back to normal.

Should there occur a drop of liquid level causing a decreased tappressure diflerential, the chain of control effects will be similaralthough in reverse to those just described.

As for the general characteristic of the function of the system hereindescribed, it should be understood that its functioning is notnecessarily dependent upon having a controlled air pressure cushionabove the liquid level in the tank, since the system is responsive tothe diflerential between the tap pressures. That is to say, a correctivelevel controllingresponse will be carried 22 What I claim is: 1. Thecombination of a liquid-treatment cell comprising a tank holding a bedof granular ion exchange material and having means for feeding liquid tothe top portion of the bed for passage downwardly therethrough, andprovided with a diaphragm-actuated eiliuent valve for controlling.

the discharge of liquid from the bottom portion of said bed whilemaintaining the bed submerged under a substantially constant pressure oigaseous medium above the liquid level in the tank, with a system forautomatically controlling said efliuent pressure of the low pressure tapit and that or the high pressure tap I! that varies. Hence this controlsystem would also operate and execute corrective settings of theellluent valve 25 even 1: the

tank were open and the liquid level exposed to atmospheric pressure.

valve through relay air pressure applied thereto in a manner to maintainsaid liquid level substantially constant relative to the top level ofthe bed; characterized by said system comprising a high pressure tapcommunicating with the interior of the tank and immersed in said liquidand in said bed, a low pressure tap communicating with the interior ofthe tank above the liquid level, said pressure taps supplying auxiliarygaseous pmsure medium below. and above the liquid level respectively andrepresenting tap pressures, a constant flow control device for eachpressure tap for supplying said auxiliary pressure medium to said tapsat a substantially constant rate, a differential pressure transmittingdevice adapted to receive the tap pressures and to emit a resultantpressure proportional to the diflerential of said tap pressures, aconduit leading from each pressure tap for transmitting tap pressure tosaid diflerential pressure-transmitting device, a controller adapted toreceive said resultant pressure and to emit a proportionate relay aircontrol pressure, conduit means for transmitting saidv resultantpressure to said controller, means for supplying relay air pressure tothe controller, means for transmitting said relay air control pressurefrom the controller to said efliuent valve to eflect control thereof inproportion to fluctuation of the liquid level in the tank. j

2. The combination according to claim 1, characterized by the fact thatthe tank is closed and that super-atmospheric pressure is maintainedabove the liquid level.

WALTER R. SWENSON.

Number Name 1,851,422 Durando Mar. 29, 1932 1,936,049 De Mers et al.Nov. 21, 1938 2,365,221 Shaior Dec. 19, 1944 2,409,768

Lavettet al. Oct. 22, 1946

